Ficolins and the Recognition of Pathogenic Microorganisms: An Overview of the Innate Immune Response and Contribution of Single Nucleotide Polymorphisms

Figure 1

Ficolin structure and the lectin complement pathway. (a) MBL is composed of a cysteine-rich region, a MASP-interacting collagenous region, and a pathogen-binding carbohydrate recognition domain. Ficolins have structural similarity to MBL, albeit the carbohydrate recognition domain is replaced by a fibrinogen-like domain. (b) There are three main pathways of complement activation: the classical, lectin, and alternative pathways. Ficolins interact with MASPs to cleave C4 and C2 to form the C3 convertase C4bC2a. This results in the cleavage of C3 into C3a and C3b. C3b then functions as an opsonin or enters the alternative pathway forming an amplification loop. Each pathway can also result in the formation of the membrane attack complex following the cleavage of C5 by the C5 convertases C4bC2aC3b or C3BbC3b and subsequent association with C6, C7, C8, and C9.

(a)

(b)